For example, in a spool-type solenoid valve for hydraulic control shown in JP 2007-285457, it is necessary to increase a controlled flow amount of the solenoid valve for improving response characteristics of controlled hydraulic pressure. Therefore, it has conventionally been dealt with by expanding a valve opening amount of a valve portion, and expanding a flow passage cross-sectional area of each port of a valve sleeve, which is another hydraulic pressure route.
However, when the controlled flow amount is increased, there may be a risk to cause problems such that controllability is destabilized due to an increase in fluid force associated therewith and that contamination resistance is declined due to an increase in contamination amounts passing through the valve portion.